In conventional planar lightwave circuits (PLCs), light is confined to either an optical slab or waveguide, defined by a core region, possessing a higher reflective index contrast relative to surrounding cladding material, e.g. upper, lower and sidewall cladding. The optical core runs parallel to the wafer surface, thus restricting the light to a propagation direction that is predominantly parallel to the wafer surface. The direction of the light propagation largely favors integration of planar lightwave circuits with a certain type of active component, such as waveguide photo-detectors and edge-emitting lasers, both of which rely on the light propagating parallel to the wafer surface. However, many other active components, most notably surface photo-detectors and vertical-cavity surface emitting lasers (VCSELs) require that the light enters or exits the chip in the direction that is largely perpendicular to the wafer surface, which makes it difficult to integrate surface photo-detectors and VCSELs with planar lightwave circuits.
Furthermore, certain active components require that the light undergoes filtering before being coupled into the planar lightwave circuits. For example, there might be a need to perform filtering of light before it can be coupled with a surface photodetector. Conversely, emission from the VCSEL might require filtering of amplified spontaneous emission (ASE) or wavelength locking before it can be integrated with a planar lightwave circuit. For a diverging light having wide angular content (as opposed to plane wave), e.g. light exiting a waveguide core, it is advantageous to position the filter perpendicular to the propagation direction of the light, as described in this invention. Perpendicular-oriented filter provides the most consistent performance for the spectral response of light entering the filter at various angles.
Consequently, there is a need for an integrated reflector that can enable integration of surface photodetectors and VCSELs with a planar lightwave circuit, as well as to provide additional functionality, such as filtering of light.
An object of the present invention is to overcome the shortcomings of the prior art by providing a vertical reflector chip, which enables the light to exit the optical plane within a planar lightwave circuit. The vertical re Hector can optionally have a thin film coating that enables filtering of light of specific wavelength.